The invention relates to a transmission and optionally reception head incorporating an optical fibre portion. It more particularly applies to an opto-electronic head using a light-emitting diode having a relatively large photoemissive surface and an only slightly directional radiation diagram coupled to a fibre with a diameter smaller than 400 microns, for example an optical fibre with a core diameter of 50 to 200 microns.
The invention also relates to a connection device incorporating such a head.
In optical telecommunications on the transmitter side, there is electronic modulation equipment, called the module and then an opto-electronic emission head associating a photoemissive diode with an optical fibre portion. This portion is generally very short and is incorporated in a fibre holder, which can constitute a male or female member of an optical fibre connector.
In the case of very short distance connections (a few dozen to a few hundred meters) a light emitting diode is generally joined to an optical fibre with a diameter exceeding 400 microns in an emission head using relatively simple and inexpensive conventional technology.
In the case of long distance connections (a few dozen to a few hundred kilometers and in the latter case with amplification at intermediate points) a laser-type diode is joined to a fibre of diameter 50 to 100 microns. The emission head is also of a conventional nature, but utilizes high precision and consequently high cost technology.
In the case of medium distance connections of a few kilometers, it would be economically interesting to use the same technology as for short distances and to join a low cost light-emitting diode to a small diameter optical fibre, namely less than 400 microns to obtain transmission quality characteristics permitting the connection without intermediate amplification.
Unfortunately, the use of this technology then becomes difficult due to a certain number of constructional problems and in particular:
1. As the light-emitting diode has approximately the same diameter as the optical fibre, maximum accuracy is necessary, particularly with regard to the centering of the diode and the fibre holder drill hole. In conventional technology, ordinary mechanical adjustments (in statics) do not make it possible to obtain this accuracy and adjustments must be carried out in operation on each individual head (in dynamics), i.e. whilst controlling the transmitted light. This procedure greatly increases the cost of the emission head.
2. As the optical fibre has a very small diameter and as the fibre holder must have a certain length so that it can function as a connector, the fibre holder must have a hole (approximately of diameter 200 microns) which cannot be drilled over such a length (a few millimeters) by conventional means.